Breast cancer is wide-spread and lethal. The most successful breast cancer treatment therapies are combination therapies in which two or more drugs, which have complementary mechanisms of action, are applied to treating cancer. This requires identification of patient subgroups that can benefit most from a set of chemotherapeutic agent and tumor-specific agent. Additionally targeted delivery represents a highly desirable treatment method in which the drug nanoparticles are designed to attach preferentially to the tumor cells. Applying this technique however requires an understanding of the target tumor cells as well as their interaction with their environment and this requires a well-designed in vitro model to test and confirm the targeted drug delivery process. This application aims to develop and validate a new in vitro tumor model system for breast cancer. This model will utilize microfluidics and tissue engineering in order to recreate tumor microenvironments. The new model system is designed to create the environment where cancer cells are grown by incorporating 3D ECM along with perfusion of interstitial fluid and co-culture with endothelial cells and stromal fibroblasts. This model system will aid in assaying tumor micro-environmental parameters to guide the selection of optimum drug combinations and design of targeted delivery systems.